Method and apparatus for improving bearing strength of piles in permafrost

ABSTRACT

A pile has a lower portion insertible into the permafrost or permanently frozen region of the soil, an intermediate portion extending through the seasonal frost or seasonal-thaw region and an upper portion exposed to the atmosphere above the soil. The lower portion is provided with cylindrical or segmented cylindrical rings which extend radially outwardly beyond the surface of the pile. The piles are used in a method of improving the bearing strength of the pile by inserting into a hole down into the permanently frozen region a pile having laterally extending rings or segments of rings on its lower portion below the seasonal-thaw region and then filling the hole surrounding the pile with fill material which eventually freezes and becomes an integral part of the permafrost soil surrounding the hole.

United States Patent Long Dec. 19, 1972 [54] METHOD AND APPARATUS FOR IMPROVING BEARING STRENGTH OF PILES IN PERMAFROST [72] Inventor: Erwin L. Long, 5741 College Drive,

Anchorage, Alaska 99504 [22] Filed: Feb. 10, 1971 [21] Appl. No.: 114,258

[52] US. Cl ..61/46, 61/36 A, 61/50,

61/53, 61/535 [51] Int. Cl. ..E02d 3/12, E02d 5/48, E02d 27/30 [58] Field of Search ..61/53, 53.5, 53.52, 53.64,

[56] References Cited UNITED STATES PATENTS R18,893 7/1933 Takechi ..6l/53 3,217,791 11/1965 Long ..l65/45 FOREIGN PATENTS OR APPLICATIONS 431,069 7/1935 Great Britain ..6l/53 OTHER PUBLICATIONS World Oil (pub.) May 1969, p. 89, 90, 91.

Primary ExaminerJacob Shapiro Attorney-Seed, Berry & Dowrey [57] ABSTRACT A pile has a lower portion insertible into the permafrost or permanently frozen region of the soil, an intermediate portion extending through the seasonal frost or seasonal-thaw region and an upper portion exposed to the atmosphere above the soil. The lower portion is provided with cylindrical or segmented cylindrical rings which extend radially outwardly beyond the surface of the pile. The piles are used in a method of improving the bearing strength of the pile by inserting into a hole down into the permanently frozen region a pile having laterally extending rings or segments of rings on its lower portion below the seasonalthaw region and then filling the hole surrounding the pile with fill material which eventually freezes and becomes an integral part of the permafrost soil surrounding the hole.

4 Claims, 6 Drawing Figures PATENTED [1E0 19 1912 FIG 4 FIG 5 M 5 l IZ INVE 0 ERWIN L. L

A TTORNEYS METHOD AND APPARATUS FOR IMPROVING BEARING STRENGTH OF PILES IN PERMAFROST BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to apparatus and methods for improving the bearing strength of piles in soil having a permanently frozen region and a seasonal-thaw region.

2. Description of the Prior Art U.S. Pat. No. 3,217,791 discloses a pile suitable for use in arctic soils which remain substantially frozen throughout the year. The patent teaches the concept of drawing cold from the atmosphere to maintain the permafrost in a frozen state around the pile even though the pressure on the soil beneath and adjacent the pile is increased due to the weight of the load supported by the pile. The purpose of the structure in this patent basically is to produce an annual net outflow of heat from the soil. The benefits then realized are a reduction in the temperature of the permafrost, an increase in the strength of the permafrost, a decrease of frost jacking, a reduction of the depth of the seasonal-thaw region andan increase in lateral pile stability.

In ordinary solid piles used in permafrost and to a minor extent in the hollow pile of US. Pat. No.

3,217,791 the surface treatment of the exterior surface of the pile will lower the adfreeze strength of the soil. (The adfreeze strength is defined as the frictional shear strength between the permafrost or frozen fill material and the solid object.) As a result the bearing strength of the pile is decreased. Using ordinary solid pile the permafrost immediately around the pile is often thawed due to the thermal conductivity of the pile in relatively warm atmospheric temperatures reducing the shear strength of the soil. Additionally the intermittent freezing and thawing of the seasonal-thaw region tends to work against the surface of the piles in effect jacking the pile upwardly.

One attempt to reduce the problems discussed above has been to add a large plate to the bottom of the pile. Although this gave some increase in bearing strength to the pile it could only increase the effective bearing area of the pile to a small extent and also relied solely on compressive bearing strength rather than frictional shear strength, an important difference as will be later pointed out. In addition, use of a large plate increased the already high costs of construction in permafrost soils because a costly large diameter hole had to be bored to accommodate the plate.

SUMMARY OF THE INVENTION It is an object of this invention to provide a pile and a method of using a pile in permafrost which reduces the effect of thawing immediately surrounding the pile.

It is another object of this invention to provide a pile and a method of using a pile in permafrost which reduces the effect of pile surface treatment.

It is another object of this invention to provide a pile and a method of using a pile which reduces seasonal jacking forces due to the intermittent freezing and thawing in the seasonal-thaw region.

It is another object of this invention to increase the bearing strength of a pile by increasing its effective outside diameter and by utilizing the shear strength of the soil for stability.

It is another object of this invention to provide a method of using a pile in permafrost by decreasing soil salinity and increasing the soil shear strength of the soil immediately surrounding the pile.

Basically the pile which can be of any cross-sectional shape includes a lower portion provided with laterally extending appendages which are all located below the seasonal-thaw region of the soil. An intermediate portion of the pile in the seasonal-thaw region directly above the permanently frozen region is left free of appendages. In the method the pile is placed in a hole and the hole surrounding the pile is filled with material that once frozen becomes integrally interconnected with the permanently frozen soil surrounding the hole and with the pile between its lateral appendages.

In one form of the invention the appendages are circular rings. In another form they are segments of circular rings. Other shapes of appendages may also be employed so long as they increase the effective diameter of the pile and preferably can trap the fill material therebetween. The rings and ring segments in the preferred form have an upward camber on their lower surfaces to prevent the entrapment of air or water between them and the surrounding soil.

In the preferred form of the method the fill material may be aggregate, or even water, having a low salinity thus increasing its freezing temperature or may be aggregate or soil of a higher shear strength than the surrounding soil.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of a vertical section of apile used in the method and embodying the principals of the invention.

FIG. 2 is an enlarged fragmentary section illustrating the positive camber of one of the rings or ring segments of the pile shown in FIGS. 1 and 3.

FIG. 3 is an isometric of a portion of a pile employing ring segments.

FIG. 4 is an operational schematic illustrating the steps of boring a hole and inserting the pile into the hole with the lateral appendages below the seasonalthaw region.

FIG. 5 is an operational schematic illustrating the step of the method wherein soil or gravel are placed in the hole around the pile with the rings below the level of the seasonal-thaw region.

FIG. 6 is an operational schematic illustrating the final step of the method wherein the fill around the pile becomes frozen to form an integral connection between the pile and permafrost.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As best shown in FIG. 1 the soil in whichthe pile is to be used includes a seasonal-frost or seasonal-thaw region l0 and apermafrost or permanently frozen region 12. The limits of the seasonal-thaw region are the surface 14 of the soil and the general dividing line 16 separating the seasonal-thaw region from the permanently frozen region. In practice, it should be understood that the depth of the line 16 will vary depending on the climatic conditions in any particular year. The seasonal-thaw region is that portion of the soil which freezes during the cold arctic winters but thaws during the summers whereas the permanently frozen region remains frozen year around.

' A pile 20 includes an upper portion 22 exposed to the atmosphere, an intermediate portion 23 located in the seasonal-thaw region and a lower portion 24 located .in the permanently frozen region. Any type of pile may be used, the one shown being of the type described in U.S. Pat. No. 3,217,791 and having a generally cylindrical hollow, metallic shell. The principles of the invention are equally applicable to wooden, concrete or other solid piles.

The lower portion 24 of the pile 20 is provided with a plurality of appendages such as longitudinally spaced rings 26 permanently secured thereto as by welding. The underside (FIG. 2) 26a of each ring has a positive upward camber of a few degrees so that air or water will be able to rise along the undersurface and escape.

FIG. 3 illustrates modified lateral appendages in the form of ring segments 28. These ring segments are spaced longitudinally along the pile alternating on opposite sides of the pile. Although not shown in detail it is to be understood that the underside of the ring segments 28 may also have an upward camber as in the preferred embodimentqlt will also be understood that the ring segments will not extend above the permanently frozen region of the hole.

In the method of the invention a hole is dug through the seasonal-thaw region into the permanently frozen region 12 and is large enough to receive the pile with the rings or ring segments integrally attached. The lower portion 24 of the pile is completely below the seasonal-thaw region. Next a slurry of fill material e.g., soil, aggregate or water is introduced into the hole around the pile. Preferably the till material is treated or selected to have a low salinity, and if desired, may be a high shear strength soil or aggregate. Finally the fill material is frozen to form an integral attachment between the rings, the cylindrical outside surface of the pile and the permafrost soil.

As is obvious the jacking forces in the seasonalthaw region will be effectively reduced since the main securement of the pile with the soil will be in the generally permanently frozen region. Thus the freezing and thaw in the seasonal-thaw region will cause the till material in that region to slide over the outside surface of the pile rather than to work the pile up or down. Since the rings become permanently locked in the fill material the till material between adjacent rings becomes trapped and in effect becomes a lateral extension of the pile. As a result the effective outside diameter of the pile becomes increased. This increase in effective outside diameter obviously increases the surface area between the material trapped by the rings and the surrounding soil thus providing an increased frictional surface area to reduce movement of the pile in the hole. In fact it has been found that the frozen fill material may actually shear at the diameter of the hole rather than at the lateral edges of the rings thus further increasing the effective shear area. Another advantageous feature is that the material trapped between the rings and thus moving with the pile has a higher frictional surface than does the surface of the pile itself. This material to soil friction further increases the bearing strength of the pile. Since this entrapped material between the rings is an insulator the effect of thawing immediately adjacent the surface of the pile is reduced since the outside surface of the material trapped between the rings oftentimes remains frozen even though its inside surface against the pile becomes thawed. The material still frozen and trapped between the rings causes the pile to be remained locked to the soil surrounding the hole. in addition, since the shear strength of soil and other materials increases with decreasing temperature and the material between the lateral outer edges of the rings will be colder than that abutting the pile, the shear strength of the material is increased. Since the fill material may be controlled both in shear strength and in salinity it oftentimes will remain frozen at temperatures higher than thawing temperature of the soil around the hole.

Since the result of using the pile of U.S. Pat. No. 3,217,791 is to permanently decrease the temperature of the permafrost soil it can be readily seen that this pile plus the use of lateral appendages according to the principles of this invention produces a combined result greatly exceeding the separate use of either. For example, by raising the level of the permanently frozen region or lowering the temperature thereof and using lateral appendages a shorter pile can be used to obtain the same bearing strength as either separately thus reducing material costs and costs of boring, filling, etc.

While a preferred form of the invention has been illustrated and described it should be understood that the invention is not to be limited thereto. E.g. the lateral extensions need not be circular rings or ring segments but may be any shape sufficient to increase the effective outside diameter of the pile and be suitable for entrapping a portion of the fill soil therebetween. In addition, it should be understood, that the effective outside shape of the pile may also be varied by enlarging the outside dimensions of the rings with increasing depth of the pile to increase resistance to uplift of the pile or increasing the lateral dimensions of the rings towards the top of the lower portion 24 to increase bearing capacity. The scope of the invention, therefore, is tobe limited only by the broadest interpretation of the claims appended hereto.

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A method of increasing the bearing strength of a pile in soil having a permanently frozen region and a seasonal-thaw region comprising adding lateral appendages to a pile, providing a hole of a diameter substantially greater than the diameter of the lateral appendages on the pile and surrounded by a permanently frozen region and a seasonal-thaw region above the permanently frozen region, inserting the pile in the hole to a depth in which the appendages are below the seasonal-thaw region, filling the hole aroundthe pile and the perimeter of the appendages to provide a stable unsheared surface between the pile and appendages and the sidewalls of the hole, and freezing the fill material in the hole to provide an integral bond between the appendages, fill material and permafrost soil surrounding the hole.

2. The method of claim 1 wherein the material in the hole around the pile has a lower salinity than that of the permafrost soil.

that removes heat from the permafrost and fill material so that the temperature is lowered in thefill material to increase its shear strength at the lateral edges of the appendages. 

1. A method of increasing the bearing strength of a pile in soil having a permanently frozen region and a seasonal-thaw region comprising adding lateral appendages to a pile, providing a hole of a diameter substantially greater than the diameter of the lateral appendages on the pile and surrounded by a permanently frozen region and a seasonal-thaw region above the permanently frozen region, inserting the pile in the hole to a depth in which the appendages are below the seasonal-thaw region, filling the hole around the pile and the perimeter of the appendages to provide a stable unsheared surface between the pile and appendages and the sidewalls of the hole, and freezing the fill material in the hole to provide an integral bond between the appendages, fill material and permafrost soil surrounding the hole.
 2. The method of claim 1 wherein the material in the hole around the pile has a lower salinity than that of the permafrost soil.
 3. The method of claim 1 wherein the fill material in the hole around the pile has a shear strength greater than the permafrost soil surrounding the hole.
 4. The method of claim 1 wherein the top of the pile is exposed to the atmosphere and the pile is of a type that removes heat from the permafrost and fill material so that the temperature is lowered in the fill material to increase its shear strength at the lateral edges of the appendages. 